Building materials using natural lumbers have a problem in that the shape or the texture of the building materials is easily damaged due to water or sunlight. For this reason, much research has been carried out to develop a wood plastic composite lumber that can eliminate the problem of the natural lumbers. The wood plastic composite lumber is manufactured by mixing granular or pellet-shaped wood fiber and synthetic resin at a predetermined mixing ratio, adding various additives according to the use of products, and forming the mixture into the shape of a panel using extrusion or injection.
In the wood plastic composite panel manufactured as described above, however, the synthetic resin, which is a matrix component of the resin complex, constitutes an outer layer on the surface of the panel after the extrusion. As a result, the appearance and the texture peculiar to the natural lumber are not provided due to the oil-like tactile sensation and high gloss peculiar to the plastic although the wood fibers are used as a filler. Consequently, various attempts have been made to solve the problems of the wood plastic composite panel.
Specifically, several attempts have been made to provide the appearance and the surface texture of the natural lumber to the wood plastic composite panel. For example, a method of performing extrusion using pigment having different colors, a method of manually processing a wood pattern, a method of transferring or printing a wood pattern, and a method of laminating films having a wood pattern of natural lumbers or artificial materials have been usually used. However, these methods have problems in that the manufacturing process is very complicated, and, in some cases, the durability of products is lowered.
In order to solve the above-mentioned problems, there have been proposed new methods that are capable of providing the texture maximally similar to the cut-open surface of the natural lumber to the surface of the wood plastic composite lumber. A representative example of the proposed methods is a method of forming a repetitive embossed pattern on the surface of a wood plastic composite lumber moving in a predetermined direction by vertically pressing a circular roll having a predetermined embossed carving and depressed carving set toward the surface of the panel from above or rotating the circular roll at high speed using a power transmission unit. This method of forming the embossed wood pattern on the surface of the panel may be performed after the extruded panel is cut into a predetermined size.
The wood plastic composite panel is provided at the surface thereof with a pattern similar to the wood pattern. However, the wood plastic composite panel has high gloss, and, when a user touches the wood plastic composite panel, oil-like tactile sensation peculiar to the synthetic resin is felt by the user. As a result, the provision of luxury appearance and texture of the natural lumber is limited although the provision of the wood pattern is possible.
In the case of a natural lumber panel manufactured by directly processing a natural lumber, excellent appearance and texture are provided after the surface of the manufactured natural lumber panel is smoothly processed. Consequently, a high-quality natural lumber panel, the surface of which has been sophisticatedly treated, is usually used for interior and exterior decorations of buildings. The surface-treated natural lumber panel has a beautiful wood pattern, a smooth and soft tactile sensation, and appropriate gloss. As a result, it is possible to represent the wood pattern. This is caused by the unique physical properties of a cellulose polymer constituting the lumber and complex actions of the natural lumber tissues.
When the surface of a wood plastic composite lumber is smoothly treated in the same manner as the natural lumber, on the other hand, the wood plastic composite lumber has high gloss and oil-like tactile sensation peculiar to the synthetic resin.
Consequently, the necessity of a technology for providing the appearance and the texture similar to the cut-open surface of a natural lumber at low costs although a resin complex including synthetic resin and wood fiber is used as a material is very high.